A carbon-13 NMR shielding study of the water-sodium octanoate-pentanol, and water-sodium octanoate-decanol systems

The 13C NMR chemical shifts on both soap and alcohol carbons have been studied as a function of solution composition for the isotropic solution phases of the three-component systems sodium octanoate-pentanol-water and sodium octanoate-decanol-water. For aqueous sodium octanoate solutions the influence on the 13C chemical shifts of solubilization of cyclohexane, p-xylene, and N,N-dimethylaniline was investigated as well as the effect of addition of sodium chloride. In general the 13C shielding is sensitive to concentration changes and from a discussion of the origin of 13C chemical shift changes it is found that the results provide information inter alia on alkyl chain conformational and polar end environmental changes. For water-rich solution phases, micelle formation, alcohol solubilization, and sodium chloride addition are all found to lead to an increased fraction of trans conformers in the soap alkyl chains. The soap alkyl chain flexibility seems to be greater for solutions containing reversed micelles than in normal micellar solutions for the nonpolar end, while there is no great difference between the two types of micelles in regard to the polar end. Studies of the carbonyl resonance of octanoate reveal considerable environmental alterations in both normal and reversed micelles and chemical shifts from the solubilizates give some insight into their solubilization state. An interaction between alcohol hydroxyls and soap carboxylate at the micellar surface is indicated. © 1978 Academic Press, Inc.